The objective is to publish in concert with histologists in human medicine and zoology, a common, comparative mammalian histological nomenclature based on the human species but also including terms unique to domestic, laboratory, and exotic animal species. The first phase of this objective has been achieved, and progress is underway on the second of three phases. The human and veterinary histology nomenclature groups, which worked separately for five or more years on their respective Nomina Histologica (NH) and Nomina Histologica Veterinaria (NHV) lists of terms now have produced a common Comparative Mammalian Nomina Histologica. It contains terms of general interest, and those relating to human and veterinary histology. The second phase consists of extending the terminologic coverage to laboratory and exotic animal species. This is being done by a systematic library search of micromorphology journals for new and previously overlooked histologic terms. Lists of the terms are sent to committee members for evaluation and reply. The third phase consists of two parts. First the editors of morphology journals have been asked by letter to obtain and evaluate the Nomina Histologica for its reasonableness and usefulness, and to offer suggestions for its improvement. Second, the collaborators on this project hope to be present at the world meetings of the human (Moscow 1979) and veterinary (Mexico City 1980) anatomists executive committees in order to expedite the approval of the common Comparative Mammalian Nomina Histologica.